Using a data sample of pp collisions corresponding to an integrated luminosity of $3~ rm fb^{-1}$, the $Xi_b^-$ and $Omega_b^-$ baryons are reconstructed in the $Xi_b^- rightarrow J/psi Xi^-$ and $Omega_b^- rightarrow J/psi Omega^-$ decay modes and their lifetimes measured to be $tau (Xi_b^-) = 1.55, ^{+0.10}_{-0.09}~{rm(stat)} pm 0.03,{rm(syst)}$ ps, $tau (Omega_b^-) = 1.54, ^{+0.26}_{-0.21}~{rm(stat)} pm 0.05,{rm(syst)}$ ps. These are the most precise determinations to date. Both measurements are in good agreement with previous experimental results and with theoretical predictions.
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